This invention relates to a backing material for a carpet underlay and more particularly to such a backing material which is a composite sheet material comprising rows of stitches formed in a base crepe paper sheet.
The present Applicants previously developed a stitched crepe paper as a backing material for a carpet underlay, as described and claimed in U.K. Pat. No. 1,422,940. This stitched crepe paper product has a dimensional stability and is capable of adhesion to a sheet of foamed or sponge rubber, both of which qualities are particularly desirable in a backing for a carpet underlay.
When used as a backing material for carpet underlay this stitched crepe paper product has been supplied by Applicants with a series of rows of perforations between the rows of side-by-side stitches. The rows of perforations were introduced into the stitched crepe paper product following complaints that squeaking tended to occur when pressure was applied to the carpet underlay by persons walking thereon. Following the introduction of the rows of perforations, the tendency to squeaking was eliminated, and the stitched crepe paper has therefore always been provided with at least one row of perforations between adjacent rows of stitches.
The rows of perforations in the stitched crepe paper have been made by unthreaded needles mounted on the needle bar of the sewing-knitting machine on which the stitched crepe paper product is manufactured. In practice this is readily done by simply providing no thread for, for example, alternate needles on the needle board, although alternative commercial products have been produced by providing thread for, in one case, only one needle in three and, in another case, only one needle in four of the needles on the needle bar of the sewing-knitting machine.
It was surprisingly found that the stitched crepe paper with the rows of perforations alternating with the rows of stitches has a higher tensile strength in the longitudinal direction, that is to say in the direction of the rows of stitches, than a stitched crepe paper which has no perforations in addition to those made in the course of stitching the crepe paper.
However, the presence of perforations in the stitched crepe paper has the disadvantage of impairing the appearance of the carpet underlay. This is a particular disadvantage when heavier weights of crepe paper are used, for example when paper of a base weight of 67 gms/m.sup.2 creped to 88 gms/m.sup.2 is used the perforations tend to be more variable in size and more noticeable than when a paper of base weight 39 gms/m.sup.2 creped to 72 gms/m.sup.2 is used. The larger holes which tend to be made by the unthreaded needles piercing the heavier papers make the presence of the coloured rubber of the carpet underlay more noticeable and the whole product less attractive visually. The appearance of the carpet underlay is commercially important, even though the carpet underlay is not visible when in use under a carpet.
Accordingly the problem has arisen of providing a backing material for a carpet underlay which is of pleasing appearance and which is not subject to any significant reduction in longitudinal tensile strength relative to the perforated backing materials currently used, and which also is not subject to undesirable squeaking when pressure is applied in use.
Surprisingly it has been found that this problem can be solved by providing deformations or embossed projections in rows lying between the side-by-side rows of stitches in a stitched crepe paper sheet material.